Gasoline is defined as a complex mixture of hydrocarbons that is used as fuel for internal combustion engines. Gasoline manufactured today is derived from petroleum and is used in automobile, aircraft, marine engines and small engines designed for miscellaneous end-uses. The composition and characteristics of gasoline vary with the source, manufacturing method and end-use requirement of the product.
Gasoline was initially produced by the simple distillation of crude oil. The types of hydrocarbons found in such "straight-run" gasolines include paraffins, aromatics and napthenes (e.g., cycloparaffins). The number of carbon atoms in the hydrocarbon fraction molecules falling within the gasoline boiling range is usually from about C.sub.4 to C.sub.12.
Today, gasoline is produced in petroleum refineries by a plurality of processes. For example, fractional distillation is still used as one refinery method for gasoline production. However, the gasoline mixtures so produced are usually light in octane content and are therefore normally supplemented with gasolines produced by other methods to increase the octane content.
Other production methods include pyrolytic cracking wherein higher molecular weight hydrocarbons, such as those in gas oils, are either catalytically cracked or thermally cracked. Reforming is used to upgrade low-octane gasoline fractions into higher octane components by use of a catalyst. Alkylation of C.sub.3 and C.sub.4 olefins with isobutane is also practiced to provide a high octane content gasoline source.
Stripper gasoline is obtained by a process that uses steam injected into a fractionator column with the steam providing the heat needed for separation. The gasoline can come from either a hydrodesulfurizer (HDS) unit or a fluidized catalytic cracking (FCC) unit. Normally, stripper gasoline from a FCC unit is highly unstable and only small percentages thereof can be blended with a more stable gasoline product in order to obtain the final motor fuel product.
In isomerization techniques, low octane paraffins are converted to longer branched chain isomers. For instance, two hydrocarbon fractions such as isobutane and propylene are commonly combined to form isooctane in a process referred to as dimerization.
Despite the particular method of production, gasolines generally suffer from oxidative degradation. That is, upon storage, gasoline can form gummy, sticky resin deposits that adversely affect combustion performance. Further, such oxidative degradation may result in undesirable color deterioration.
Accordingly, it is an object of the present invention to provide a treatment for improving the oxidative stability of gasoline mixtures. Of even more importance is the provision of such a stabilizing treatment that is effective even when highly unstable gasoline mixtures, such as those formed via stripper and pyrolysis techniques, are treated.